[AlwaysSAI]

SAI is dicussed earlier in the thread, so here's Phi Sig's story:

The Founders
The story of Phi Sigma Pi National Honor Fraternity actually begins well over
100 years ago. In 1892, the Missouri Beta Chapter of Phi Lambda Epsilon
was organized as the first fraternity at the State Teachers College at Warrensburg, Missouri (known today as Central Missouri State University). In the spring of 1914, the chapter was disbanded, but from its ashes rose a new group; an organization focused on strong academic achievement, service to mankind, and a celebration of fellowship. Several members of Phi Lambda Epsilon, along with other male students, took their plans for this new fraternity to the faculty.
At first, the faculty did not look favorably on this endeavor, mostly because of the recent closing of Phi Lambda Epsilon. However, three influential men gave their support and encouragement to this fledgling group. The faculty was swayed by these three men into granting the establishment of the new fraternity, and on February 14, 1916, Phi Sigma Pi was born. These three men were the fraternity’s founders, Dr. Eldo L. Hendricks, Dr. Claude A. Phillips, and Dr. C. H. McClure.

The Birth of Phi Sigma Pi
On February 14, 1916, Phi Sigma Pi was founded and originally named Phi
Sigma Pi Honorary Professional Fraternity. The three founders decided that
Phi Sigma Pi would stress not only scholarship, leadership, and fellowship, but
do so in a concept of an equal tripod dedicated to these three ideals. Dr.
Hendricks, the leading force behind the creation of Phi Sigma Pi, was the first
person to sign a Phi Sigma Pi roll book and is therefore known as Alpha 1. He
was followed by Dean Phillips and Professor McClure. In addition to the three
faculty members, the first chapter included ten undergraduate and honorary members.

Phi Sigma Pi Goes Co-Ed (1976 – 1979)
Late in 1975, East Carolina University contacted the Tau Chapter to inform
them they were in violation of Final Title IX Regulation Implementing Education
Amendments of 1972 Prohibiting Sex Discrimination in Education (hereafter
referred to as Title IX). After consulting with the United States Department of
Health, Education and Welfare, it was concluded that the national organization must allow Tau Chapter to admit eligible women or the chapter would cease to exist by July 1, 1976. Under Title IX guidelines, Phi Sigma Pi, as an honor
fraternity, would be required to become coeducational since remaining an allmale organization would have a discriminatory effect upon the future career
opportunities of eligible women (social fraternal organizations are exempt from
Title IX). At the October 7, 1977, National Convention in Washington, D. C., under the leadership of President Richard J. Donald, Iota 800, the National Constitution was amended to admit eligible women, thus ensuring that Phi Sigma Pi would remain an honor fraternity. Women were admitted into Phi Sigma Pi beginning in the fall semester of 1977. Alpha Chapter was reactivated coeducational and Brother Laura Abney became the first woman to be inducted. Tau Chapter was the first existing chapter to induct a female Honorary Brother, Clauda Pennock Todd, Tau 879. The other chapters gradually went coeducational, with Sigma Chapter being the last all-male chapter to admit women in the autumn of 1989. The word, “Brother,” would now come to mean both men and women. The decision to admit females had an enormous impact on Phi Sigma Pi, both in the 1970’s and today. This decision was not welcomed with open arms by the majority of the Phi Sigma Pi Brotherhood. In an excerpt from a letter to the National Office written by a chapter president, it was said “…we are signing our own bill of execution and are baring our necks to the axe. We foresee a fast-approaching end to a fine, outstanding sixty year tradition which has, on our campus, designated a body of exemplary men.” Barry Mitsch, Tau 826, was the initiate advisor when “Sweetheart” was inducted as an Honorary Brother into Tau Chapter. “We were entering the unknown, and it was a challenging time. The fraternity broke into two camps, one that did not want to admit women and was even willing to lose university recognition, and one that understood the need to change. I think the induction of Sweetheart was part of the healing process. I remember it as a joyous occasion. She was quite a remarkable lady in her own respect but usually stayed in the background. Dr. Todd had such big energy, and Sweetheart was the perfect sidekick.”
Today, of course, history tells us that admitting females had an overwhelmingly positive impact on the growth and development
of Phi Sigma Pi. But in the late 1970’s, this seemingly radical change
was difficult for many Brothers to accept. Many Brothers left the fold, and by
1980, only eight chapters remained; Theta, Iota, Pi, Sigma, Tau, Phi, Alpha Alpha and Beta Gamma Chapters.

The above taken from the "Scholar's Province"--the official pledge manual of the fraternity.

Long story short--In the years to follow, under the guidance of many dedicated brothers the fraternity saw many dormant chapters reactivated. And, by the 1990's we were growing by an average of 8 chapters a year.